Fiddly Physics - Writers Forum

Twistedtree · 03-26-2008, 11:15 AM

I'm currently writing a car chase scene, in which two of the vehicles engage with small arms fire. I have a number of questions.

I know the muzzle velocity of one of the weapons used is 905m/s. How will this change if the target and gun are moving in an opposite direction to the bullet at a roughly steady speed? I assume it will have no effect?

what about the other way; the chase car firing on the runaway? The cars and bullets are now all going in the same direction. How will this effect the round?

Any rough idea's of the effects of these 5.56mm rounds hitting the front of a car? (it's a smallish people carrier)

Just thinking of it all makes my 'ickle brain hurt

Katastrof · 03-26-2008, 02:26 PM

Well I think I could answer this, but I need more information. And clarify your question; I'm not sure if you're wondering whether a bullet would slow down if fired from an opposite direction to its target or...something else entirely.

ScorpioJoe · 03-26-2008, 09:57 PM

The important thing is velocity. The car has a velocity that the gun and bullet are already traveling at. Thus, when the bullet leaves the gun. its acceleration is going to propelled it to speeds way faster than car. Also, 905 meters per second is pretty damn fast, I don't think anything can travel that fast on ground. So, really, you are worried about nothing, your car chase scene should be fine. Hope I helped.

Twistedtree · 03-27-2008, 01:21 PM

The guns used are C8 carbines. The muzzle velocity is definatly 905 meters per second. I suppose what im interested in is if the bullet will have the velocity of the car plus that of is standard velocity.

ScorpioJoe · 03-27-2008, 02:08 PM

Well, yes, but no. The initial velocity of the bullet will be that of the car, the velocity of the bullet though will be much faster than the car but you can't calculate the bullets velocity by adding the car and muzzle velocity together. The velocity of the bullet will be the cars velocity plus whatever extra velocity is added due to acceleration from the explosion in the barrel.

Katastrof · 03-27-2008, 03:06 PM

Quote:

Originally Posted by Twistedtree

The guns used are C8 carbines. The muzzle velocity is definatly 905 meters per second. I suppose what im interested in is if the bullet will have the velocity of the car plus that of is standard velocity.

Well, velocity is really not what your looking for. You're looking for the acceleration of the bullet, since velocity is relative anyway.

Twistedtree · 03-27-2008, 03:48 PM

ok, ok, i surrender. I just won't go into the details in the book.
Thanks to all that helped

Shawn · 03-27-2008, 04:22 PM

Instead of trying to explain velocity and acceleration, why not explain classical relativity... or perhaps not worry about it at all... people will get along just fine without the technical specifics of the guns or the trajectory of the bullet.

Katastrof · 03-27-2008, 04:26 PM

Quote:

Originally Posted by Shawn

Instead of trying to explain velocity and acceleration, why not explain classical relativity... or perhaps not worry about it at all... people will get along just fine without the technical specifics of the guns or the trajectory of the bullet.

Hey I would, if I had enough time...

Sam Winchester · 03-27-2008, 04:29 PM

I'm currently writing a car chase scene, in which two of the vehicles engage with small arms fire. I have a number of questions.

I know the muzzle velocity of one of the weapons used is 905m/s. How will this change if the target and gun are moving in an opposite direction to the bullet at a roughly steady speed? I assume it will have no effect?

It won't change at all, unless the car you're firing at is 900 metres away, which would mean shooting at it would be pointless anyway.

what about the other way; the chase car firing on the runaway? The cars and bullets are now all going in the same direction. How will this effect the round?

There are lots of aberrations that can affect bullet travel. Wind-speed, humidity, moisture, and others. A bullet fired from a gun with a muzzle velocity of 905 m/s at a car 200 metres away will drop maybe a quarter of an inch, perhaps more. Of course, it will also slow down.

Any rough idea's of the effects of these 5.56mm rounds hitting the front of a car? (it's a smallish people carrier)

A 5.56mm NATO round is a ghastly powerful thing. At a distance of, say, one hundred to two hundred metres, the bullet would probably penetrate the comparatively weaker sheet-metal of the bonnet. Depending on the accuracy of the shooter, he might be able to destroy the engine block with a well placed shot.

Just thinking of it all makes my 'ickle brain hurt

[/quote]

Sam.

Shawn · 03-27-2008, 04:37 PM

The rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction.

In other words, when acted upon by a force, an object's momentum will change proportionally in relation to its current momentum.

A bullet fired from a moving car will travel faster than the car, because its momentum is affected by a kinetic force (the expanding gases in the barrel) and changes in proportion to the speed of the car.

But even then, answers to physics problems are often ambiguous because there's no way to account for all variables.

So just write without the technical crap. If a bullet hits a car, it's going to hit it regardless if it's supposed to or not.

Non Serviam · 03-27-2008, 04:45 PM

We need more information to do the physics. Would have to be something like this:

Vehicle x is travelling at 10m/s. Vehicle y is travelling at 15 m/s in the same direction, starting at a point 100 m behind vehicle x. Someone in vehicle y fires a bullet at vehicle x at 905 m/s (and for the purposes of this exercise you may assume the air resistance is negligible so the bullet speed is constant)...

Vector diagrams would help even more if the vehicles aren't on a straight road.

Shawn · 03-27-2008, 04:49 PM

If I have shoe y and I hit Non Serviam x upside the head with it, how many hits (h) does it take until x perishes from internal hemorrhaging?

Sam Winchester · 03-27-2008, 05:17 PM

This is getting good. We're getting a bit of a war between the mentors here. By the way, Shawn, your post made me spit out my tea it was that funny.

Sam.

Katastrof · 03-27-2008, 06:27 PM

Quote:

Originally Posted by Non Serviam

We need more information to do the physics. Would have to be something like this:

Vehicle x is travelling at 10m/s. Vehicle y is travelling at 15 m/s in the same direction, starting at a point 100 m behind vehicle x. Someone in vehicle y fires a bullet at vehicle x at 905 m/s (and for the purposes of this exercise you may assume the air resistance is negligible so the bullet speed is constant)...

Vector diagrams would help even more if the vehicles aren't on a straight road.

Sadly I was asking for something like this...Is there such a profession as literary physicist?